1. The Field of the Invention
The present invention relates generally to the manufacture of composite tubes. More particularly, it concerns a solution to the problem of mandrel removal in the manufacture of filament wound composite tubes having a substantially constant inner diameter.
2. The Background Art
The challenges of mandrel removal in the manufacture of composite tubes are well known to those of ordinary skill in the art. A composite tube is typically constructed by winding fibrous material impregnated with a resin onto a mandrel and curing the resulting composite material while it is on the mandrel. After the composite tube is cured, the mandrel is removed.
Long composite tubes, i.e., those more than about six feet in length, are quite difficult to remove from the cured composite tube is the diameters of the mandrel and tube are substantially constant. It is known to produce the mandrel with a slightly tapered exterior which aids greatly in mandrel removal. The resulting composite tube will then be formed with a taper as well.
However, some applications simply require the composite tube to have a substantially constant diameter. Mandrel extraction devices have been designed to apply several thousand pounds of force to the cured composite tube to remove it from the mandrel. Such devices are typically designed to hold the mandrel firmly and pull the cured composite tube using hydraulic power.
Unfortunately, the presently known mandrel extraction devices are characterized by several disadvantages. The large tensile force used to pull the composite tube from the mandrel sometimes weakens and damages the composite tube. Further, the prior art mandrel extraction techniques known to applicant are simply not capable of removing composite tubes longer than about eight to ten feet that have been cured upon mandrels of substantially constant diameter.